Manufacturing method of semiconductor device

ABSTRACT

In order to provide a manufacturing method of a semiconductor device which can improve the interconnection lifetime, while controlling the increase in resistance thereof, and, in addition, can raise the manufacturing stability; by applying a plasma treatment to the surface of a copper interconnection  17  with a source gas comprising a nitrogen element being used, a copper nitride layer  24  is formed, and thereafter a silicon nitride film  18  is formed. Hereat, under the copper nitride layer  24 , a thin copper silicide layer  25  is formed.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a manufacturing method of asemiconductor device which comprises the steps of forming acopper-containing film, and more particularly to a manufacturing methodof a semiconductor device having an interconnection, an interconnectionconnecting plug, a pad section or such, made of copper or a copperalloy.

[0002] In recent years, copper and copper alloys have been widely usedas the material for interconnections and connecting plugs to achievehigher speed operations in the elements. With these metals utilized, theinterconnections and the likes are generally formed by the damascenemethod.

[0003]FIG. 5 is a series of views illustrating the steps of aconventional method of forming a copper interconnection. Now, thismethod is described below. First, as shown in FIG. 5(a), after aninsulating film 10 and an interlayer insulating film 12 are formed, inthis order, on a semiconductor substrate (not shown in the drawings), aninterconnection trench is set within the interlayer insulating film 12,and thereon a barrier metal film 14 made of Ta; TaN or such and a seedcopper film 15 are formed, in succession, and then a copper film 16 isformed by the plating method.

[0004] The semiconductor wafer 1 in this state is subjected to thechemical mechanical polishing (CMP) and copper lying outside of theinterconnection trench is removed, while copper lying inside of thetrench is left as it is, whereby a copper interconnection 17 is formed.At this, copper oxide 21 is produced on the copper interconnection 17,and a carboxylic acid cleaning is performed (FIG. 5(b)) for removingthis copper oxide 21. In this way, copper oxide which may cause anincrease in interconnection resistance or contact resistance can beeliminated (FIG. 5(c)). After that, as shown in FIG. 5(d), a siliconnitride film 18 is formed and thereon an interlayer insulating film 19is formed.

[0005] In such steps of forming a copper interconnection, it isessential to remove copper oxide which is formed on the copper surfaceso that the electrical resistance may be prevented from increasing.While copper oxide is removed with carboxylic acid in the above method,other methods such as a method by a plasma treatment with a reducing gasare also known. For example, in a method described in “TDDB Improvementin Cu Metallization under Bias Stress” by J. Noguchi et al. (IEEE38^(th) Annual International Reliability Physics Symposium, San Jose,Calif. 2000, pp. 339-343), a plasma treatment with a hydrogen or ammoniagas is carried out to achieve the reduction of CuO which is formed onthe surface of the copper interconnection to Cu, along with theformation of a Cu layer thereon. Moreover, it is described therein thatonce CuN is formed, this may function as a protective film, and when acopper-diffusion prevention film of SiN or the like is grown thereon,the CuN layer can suppress the formation of the copper silicide layer inthe copper interconnection and, therefore, can restrain the increase inelectrical resistance.

[0006] However, conventional techniques described above have thefollowing problems.

[0007] In a method comprising the step of removing a copper oxide filmwith carboxylic acid, after the cleaning to remove the copper oxide filmis carried out, the wafer is taken out from the cleaning equipment andtransferred for the step of growing the films. During the transfer, thewafer may be exposed to the air so that the copper surface therein maybe reoxidized, leading to a problem of the increase in electricalresistance and the decrease in adhesion between the copperinterconnection and the copper-diffusion prevention film formed thereon.

[0008] Meanwhile, although a method with a reducing plasma treatment cancontrol the increase in resistance in a certain degree, the methodbrings about another problem of the decrease in interconnectionlifetime. In fact, it is the present inventors who first confirmed,through experiments, that a reducing plasma treatment may lower theinterconnection lifetime, due to the electromigration or the like, andgive rise to a variation in resistance. To remove the copper oxide filmthoroughly by the plasma treatment, it is necessary to employconsiderably rigorous conditions for the plasma treatment and, as aresult, the copper surface becomes rugged. Furthermore, since thenitridation to form CuN proceeds with copper oxide still partiallyremaining on the copper surface, the film thickness of the CuN becomesnon-uniform and, herewith, the film thickness of a copper silicide layerthat is to be formed in the copper interconnection becomes alsonon-uniform. This presumably causes a lowering of the interconnectionlifetime and produces variation in resistance.

[0009] Further, in the method using the reducing plasma treatment, thereare occasions where the film thickness of the copper-diffusionprevention film becomes non-uniform, owing to the unevenness of theunderlying layer surface. This necessitates, in the later step of holeetching to form an interconnection connecting plug, to performoveretching further more so as to remove that copper-diffusionprevention film so that the degradation of the copper interconnectionsurface may be brought about by the plasma exposure.

SUMMARY OF THE INVENTION

[0010] In light of the above problems, an object of the presentinvention is to provide a manufacturing method of a semiconductor devicewhich can improve the interconnection lifetime and the variation inresistance of the copper interconnection, while controlling the increasein resistance thereof, and, in addition, can raise the manufacturingstability.

[0011] The present invention provides a method of manufacturing asemiconductor device; which comprises the steps of:

[0012] forming a copper-containing film on a semiconductor substrate;

[0013] removing, with a cleaning agent, a copper oxide on a surface ofsaid copper-containing film;

[0014] applying a nitriding treatment to the surface of saidcopper-containing film from which the copper oxide has been removed; and

[0015] forming a copper-diffusion prevention film comprising a siliconon said copper-containing film which has been subjected to the nitridingtreatment.

[0016] Further, the present invention provides a method of manufacturinga semiconductor device; which comprises the steps of:

[0017] forming a copper-containing film on a semiconductor substrate;

[0018] removing a copper oxide on a surface of said copper-containingfilm;

[0019] applying an anticorrosive treatment to the surface of thecopper-containing film, with an anticorrosive-containing solution beingused;

[0020] carrying out a heating treatment to detach the anticorrosivewhich is adhered onto the surface of the copper-containing film and,subsequently, applying a nitriding treatment to the surface of saidcopper-containing film; and

[0021] forming a copper-diffusion prevention film comprising a siliconon said copper-containing film which has been subjected to the nitridingtreatment.

[0022] Further, the present invention provides a method of manufacturinga semiconductor device; which comprises the steps of:

[0023] forming a copper-containing film on a semiconductor substrate;applying a nitriding treatment to the surface of said copper-containingfilm without allowing the semiconductor substrate to be exposed to anoxygen-containing atmosphere; and

[0024] forming a copper-diffusion prevention film comprising a siliconon said copper-containing film which has been subjected to the nitridingtreatment.

[0025] In the afore-mentioned manufacturing methods, a nitridingtreatment is applied to the surface of a copper-containing film, aftercopper oxide which is present on the surface of the copper-containingfilm is removed with a cleaning agent. Or a nitriding treatment isapplied to the surface of a copper-containing film without allowing asemiconductor substrate to be exposed to an oxygen-containingatmosphere. In the method described in the BACKGROUND, wherein a copperoxide film is removed by a plasma treatment with a reducing gas, it isnecessary to conduct the plasma treatment under somewhat rigorousconditions. For instance, in order to remove copper oxide, the plasmaatmosphere is required to have a high reducing capability. This makesthe surface of the copper-containing film rugged, causing the increasein interconnection resistance and contact resistance. Contrary to this,the plasma treatment in the present invention can be carried out undermilder conditions, because the treatment does not aim at removing copperoxide.

[0026] Further, in the afore-mentioned conventional techniques, even ifthe treatment is conducted in a plasma atmosphere with a high reducingcapability, a copper oxide film cannot help remaining in part. Asagainst this, in the present invention, since the nitriding treatment isapplied to a clean copper surface where no copper oxide film remains,the film thickness and the film quality of a CuN film which is formed bythe nitriding treatment can be made uniform and, herewith, the filmthickness of a copper silicide layer to be formed in the copperinterconnection becomes uniform. As a result, the following effects canbe attained.

[0027] First, the increase in electrical resistance which may be broughtabout by oxidation of the copper-containing film surface can besuppressed. In the afore-mentioned manufacturing methods, a protectivefilm made of CuN is homogeneously formed to an uniform thickness overthe copper-containing film so that a clean copper-containing metalsurface where no copper oxide film is formed is directly covered withthe protective film. This protects copper from oxidation with effect inthe subsequent steps, and prevents the electrical resistance fromincreasing.

[0028] Secondly, the interconnection lifetime is lengthened. In theafore-mentioned manufacturing methods, CuN is formed, while thenitriding treatment is being applied to the surface of thecopper-containing film, and once a copper-diffusion prevention filmcomprising silicon is formed, this CuN restrains silicon from diffusinginto the copper-containing film. However, CuN does not cut off thesilicon diffusion completely, and a small amount of silicon passesthrough CuN and reaches inside of the copper-containing film to form athin copper silicide layer in the vicinity of the surface of thecopper-containing film. As described above, the protective film made ofCuN is homogeneously formed to a uniform thickness so that the silicidelayer formed thereunder is a thin layer, homogeneous and having auniform thickness. The formation of such a silicide layer is consideredto be the cause for lengthening of the interconnection lifetime. Asilicide layer of this sort can be also formed by the step of forming asilicon nitride film 18, in the method described in the BACKGROUND,referring to FIG. 5. However, because silicon nitride, in this instance,is deposited without a copper nitride layer being formed, silicon thatis the very constituting material for silicon nitride diffuses into thecopper interconnection, excessively, and a thick silicide layer isformed, causing a problem of the increase in interconnection resistanceand contact resistance. Meanwhile, in the afore-mentioned method with areducing plasma treatment, the formation of a silicide layer itself isconsidered to be suppressed. Unlike these conventional techniques, inthe present invention, because a CuN layer, capable to restrain silicondiffusion appropriately, is formed, a silicide layer can be formedhomogeneously and uniformly to a thin film thickness. This enables bothobjects, an improvement of the interconnection lifetime and a loweringof the electrical resistance, to be achieved together.

[0029] Thirdly, because the copper-diffusion prevention film can beformed homogeneously and with its film thickness well under control, thedegradation of the copper-containing film in the subsequent steps can beprevented from occurring. For instance, when the present invention isapplied to a method of forming a copper interconnection, after copperinterconnection made of a copper-containing film is formed, aninterconnection connecting plug is to be formed thereon. In the step ofhole etching, thereat, it is required to remove the copper-diffusionprevention film and expose the copper interconnection. In order toremove the copper-diffusion prevention film lying in a plurality ofholes for sure, it is essential to make a certain amount of overetching.Nevertheless, in the present invention, as the copper-diffusionprevention film can be formed homogeneously and with its film thicknesswell under control, the film thickness for the copper-diffusionprevention film itself can be made thinner than the conventional one,and, as a result, the amount of overetching can be well reduced. Doingthis, the alteration of the resist form can be lessened and thelinewidth accuracy of the fabricated form, heightened. Further, thethickness of the resist can be reduced so that more minute fabricationthereof can be made. In addition, the amount of deposits generated afteretching may drop, and besides shavings and damages of the underlyingcopper interconnection due to overetching can be reduced. Further, asthe film thickness of the copper-diffusion prevention film can be setthin, parasitic capacitances between horizontally adjacentinterconnections and within the interconnection along the direction ofthe substrate thickness can be reduced. As a result, cross talk betweeninterconnections can be suppressed.

[0030] In the afore-mentioned manufacturing methods of a semiconductordevice, the nitriding treatment of the copper-containing film surfacecan be effected by a plasma treatment using a source gas comprising anitrogen element. Further, following the step of removing copper oxide,and prior to the step of applying a nitriding treatment to the surfaceof a copper-containing film, the step of applying an anticorrosivetreatment to the surface of the copper-containing film with ananticorrosive-containing solution may be carried out. Further, after thestep of applying the anticorrosive treatment to the surface of thecopper-containing film, the step of a heating treatment to detach theanticorrosive which is adhered onto the surface of the copper-containingfilm and, subsequently, the step of applying a nitriding treatment tothe surface of the copper-containing film may be carried out. Hereat, ifthe afore-mentioned heating treatment is carried out in a vacuum and,thereafter, keeping the vacuum as it is, the step of applying thenitriding treatment to the surface of the copper-containing film isperformed, the nitriding treatment can be applied to the surface of thecopper-containing film which is in a clean state, the film thickness andquality for the copper nitride layer and copper silicide layer can beadvantageously made more uniform.

[0031] As set forth above, the present invention can make the filmthickness and the film quality of CuN that is formed by the nitridingtreatment uniform and, herewith, can form a copper silicide layer to anuniform thickness in the copper interconnection. Consequently, thepresent invention can improve the interconnection lifetime, whilepreventing the resistance of a copper-containing film from increasing.Furthermore, because the present invention can form a copper-diffusionprevention film homogeneously with a film thickness well under control,it is possible to prevent the degradation of the copper containing filmfrom occurring in the subsequent steps.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The above and other objects of the invention will become apparentupon making reference to the accompanying drawings.

[0033]FIG. 1 is a series of schematic cross-sectional views illustratingthe steps of a manufacturing method of a semiconductor device accordingto the present invention.

[0034]FIG. 2 is a series of schematic cross-sectional views illustratingfurther steps of the manufacturing method of a semiconductor deviceaccording to the present invention.

[0035]FIG. 3 is a series of schematic cross-sectional views illustratingfurther steps of the manufacturing method of a semiconductor deviceaccording to the present invention.

[0036]FIG. 4 is a series of schematic cross-sectional views illustratingfurther steps of the manufacturing method of a semiconductor deviceaccording to the present invention.

[0037]FIG. 5 is a series of schematic cross-sectional views illustratingthe steps of a conventional manufacturing method of a semiconductordevice.

[0038]FIG. 6 is a pair of views in explaining a method of evaluating theinterconnection resistances and the interconnection lifetimes inExamples.

[0039]FIG. 7 is a graph showing the evaluation results of theinterconnection resistances in Examples.

[0040]FIG. 8 is a graph showing the evaluation results of theinterconnection lifetimes in Examples.

[0041]FIG. 9 is a graph showing the evaluation results of the silicideoccupation ratios in Cases for Reference.

[0042] In the accompanying drawings, referential numerals mean asfollows; 1: silicon wafer, 10: insulating film, 12: interlayerinsulating film, 14: barrier metal film, 15: seed copper film, 16:copper film, 17: copper interconnection, 18: silicon nitride film, 19:interlayer insulating film, 21: copper oxide, 22: anticorrosive, 24:copper nitride layer, 25: copper silicide layer, 27: interlayerconnecting plug.

DETAILED DESCRIPTION

[0043] A copper-containing film as used in the present invention iseither a copper film or a copper alloy film which contains at least 80wt. % of copper and preferably at least 90 wt. % of copper. A copperalloy contains, as another component, a different element such as Mg,Se, Zr, Hf, Nb, Ta, Cr, Mo, or the like.

[0044] A copper-diffusion prevention film as used in the presentinvention is a film comprising a silicon, which is set to prevent copperfrom diffusing into and within the interlayer insulating film and ismade of, for example, SiN, SiON, SiC, SiCOH or the like.

[0045] In the present invention, a solution, especially an aqueoussolution containing any of carboxylic acid compounds is preferably usedas a cleaning agent. Carboxylic acid compounds as used herein includecarboxylic acids and their salts. It is preferable to employ one or morecompounds selected from the group consisting of oxalic acid, citricacid, malic acid, maleic acid, succinic acid, tartaric acid, malonicacid and their salts. Among these compounds, oxalic acid, in particular,is preferably used owing to its effectiveness to remove copper oxide.Oxalic acid has a good capability to form a chelate complex effectivelywith copper oxide, once copper oxide is produced by the Cu-CMP.Meanwhile, copper atoms in the Cu film constituting the interconnectionare held together by the metallic bonding so that they are hard to forma complex with oxalic acid and spared from being etched. In addition,since metals such as TiN, Ta, TaN, and TaSiN that may constitute abarrier film are also hard to form a complex with oxalic acid, they arealso spared from being etched. Therefore, through the use of oxalicacid, CuOx in the form of a film and Cu particles that remain on thesurface can be selectively removed, without etching thecopper-containing film or the barrier metal film. The total content ofcarboxylic acid with respect to the whole amount of the cleaning agentis set to be preferably 0.005-10 wt. % and more preferably 0.01-1 wt. %.

[0046] The cleaning agent as used in the present invention may contain acomplexing agent. As a complexing agent, any of polyaminocarboxylic acidcompounds or ammonium fluoride may be preferably used. Amongpolyaminocarboxylic compounds, compounds such asethylenediaminetetraacetic acid (EDTA),trans-1,2-cyclohexanediaminetetraacetic acid (CyDTA), nitrilotriaceticacid (NTA), diethylenetriaminepentaacetic acid (DTPA),N-(2-hydroxyethyl) ethylenediamine-N, N′,N′-triacetic acid (EDTA-OH) andtheir salts are preferable. If a salt is to be employed, a salt thatdoes not adversely affect characteristics of the semiconductor device ispreferable, and especially a salt containing no metal such as ammoniumsalt is preferable. The content of the complexing agent to the wholecleaning agent is set to be preferably 1-10,000 ppm, and more preferably10-1,000 ppm. When this concentration is too low, a sufficient chelatingeffect cannot be obtained. On the other hand, if the concentration isexcessively high, organic materials may remain on the substrate surface,which causes deterioration of the performance of the semiconductorelement or increase in the cost required for the treatment of the wastefluid.

[0047] The cleaning agent as used in the present invention may containan anion-based or a cation-based surfactant. Examples of an anion-basedsurfactant include carboxylic acid type ones, sulfuric acid type onesand sulfuric ester type ones, in other words, acids having a —COOHgroup, a —SO₃H group and a —OSO₃H group and their salts. If a salt is tobe employed, ammonium salt or primary, secondary or tertiary amine salthaving a little adverse effect on the quality of the semiconductordevice that is the very object for the cleaning is preferable. Asspecific examples of an anion-based surfactant, there can be given, forexample, C₁₂H₂₅O(CH₂CH₂O)₂SO₃H, C₉H₁₉PhO (CH₂CH₂O)₄SO₃H,C₁₂H₂₅O(CH₂CH₂O)₄SO₃H, (Ph is a phenylene group) and their ammoniumsalts as well as their primary, secondary and tertiary amine salts.Among the above surfactants, ammonium salts of sulfuric ester and theirprimary, secondary and tertiary amine salts, which have the particularlystrong removing effect on metal contaminations adhered to the surface inthe metal region, are preferable. As examples of a cation-basedsurfactant, there can be given C₈H₁₇N (CH₃)₃ Br, C₁₂H₂₅N (C₂H₅) (CH₃)₂Br and the like.

[0048] In the present invention, the amount of the anion-based or thecation-based surfactant to be used is appropriately determined,according to the type of the surfactant, but is set to be preferably1-1,000 ppm, and more preferably 10-500 ppm, by weight, with respect tothe cleaning agent for the substrate. When the added amount is toosmall, a sufficient cleaning effect may not be obtained. On the otherhand, with an excessively large amount, the treatment of the waste fluidmay become difficult.

[0049] In the present invention, for an anticorrosive, there can be usedbenzotriazole (referred to as BTA, hereinafter), its derivatives, uricacid, its derivatives or such. Through the use of any of theseanticorrosives, excellent anticorrosive effect on the metal such ascopper can be obtained.

[0050] As a benzotriazole derivative, any of IRGAMET Series placed onthe market by Ciba Speciality Chemicals, and more specifically IRGAMET42 is preferably used. IRGAMET 42 is 2,2′-[[(methyl-1H-benzotriazole-1-yl)methyl]imino]bis-ethanol.

[0051] Examples of a uric acid derivative include: purine; derivativesof purine such as 6-aminopurine, 2-amino-6-oxopurine,6-furfurylaminopurine, 2,6-(1H,3H)-purinedione,2-amino-6-hydroxy-8-mercaptopurine, allopurinol, uric acid, kinetin,zeatin, guanine, xanthine, hypoxanthine, adenine, theophylline, caffeineand theobromine; 8-azaguanine; derivatives of 8-azaguanine; pteridine;derivatives of pteridine such as 2-amino-4,6-dihydroxypteridine,2-amino-4,7-dihydroxypteridine and 2-amino-4,6,7-trihydroxypteridine;pterin; derivatives of pterin; cyanuric acid; derivatives of cyanuricacid such as triscarboxymethylcyanuric acid and triscarboxyethylcyanuricacid; isocyanuric acid; derivatives of isocyanuric acid such astriscarboxymethylisocyanuric acid and triscarboxyethylisocyanuric acid;hydantoin; derivatives of hydantoin such as dimethylhydantoin; allantoin(5-ureidohydantoin); derivatives of allantoin; barbituric acid;derivatives of barbituric acid; nicotinic acid; and derivatives ofnicotinic acid such as isonicotinic acid and citrazinic acid. Each ofthese substances can be used independently, or two or more of them canbe used together.

[0052] Among these substances described above, purine, derivatives ofpurine, cyanuric acid, derivatives of cyanuric acid, isocyanuric acid,derivatives of isocyanuric acid, nicotinic acid, and derivatives ofnicotinic acid are preferably used, because they demonstrate excellentanticorrosive effect on the metal such as copper.

[0053] In the present invention, an anticorrosive is preferably used asan aqueous solution, and, thereat, the minimum amount of theanticorrosive to be mixed into the aqueous solution is set to bepreferably 0.0001 wt. % and, more preferably 0.001 wt. %. With such anamount mixed, the protection against corrosion can be made substantial.The maximum amount of the anticorrosive mixed thereinto is notparticularly limited and set appropriately, depending on its solubilityin the aqueous solution. The maximum amount to be mixed for BTA and itsderivatives is set to be preferably 1 wt. % or so, and the maximumamount for uric acid derivatives is set to be, for example, 20 wt. % orso, and preferably 10 wt. % or so. Hereat, an inhibitor forprecipitation of the anticorrosive, made of an amine compound or such,may be added to the anticorrosive, as the occasion may demand.

[0054] In the present invention, it is preferable that, after the stepof an anticorrosive treatment, the step of a heating treatment whereinthe anticorrosive adhered onto the surface of the copper-containing filmis detached by a heating treatment is carried out and, then, the step ofa nitriding treatment follows. Further, it is preferable that the stepof the afore-mentioned heating treatment is carried out in a vacuum and,thereafter, keeping the vacuum as it is, the step of the nitridingtreatment is performed. Since this arrangement enables the nitridingtreatment to be applied to the copper surface which is in a clean state,the film thickness and the quality for the copper nitride layer and thecopper silicide layer can be made uniform, and thus, the interconnectionlifetime can be lengthened, while lowering the interconnection contactresistance.

[0055] Next, referring to the drawings, one example of a method ofmanufacturing a semiconductor device according to the present inventionis described below.

[0056] Firstly, as shown in FIG. 1(a), on a silicon wafer, an insulatingfilm 10 and an interlayer insulating film 12 are formed in this orderand, then, a plurality of interconnection trenches patterned into aprescribed shape are formed by dry etching. For the material of theinterlayer insulating film 12, in addition to silicon oxide,low-dielectric-constant materials, for example, polyorganosiloxanes suchas MSQ (methylsilsesquioxane) and MHSQ (methylated hydrogensilsesquioxane) and aromatic organic materials such as polyallyl ether(PAE) and divinylsiloxane-bis-benzocyclobutane (BCB) can be utilized.

[0057] Next, after a barrier metal film 14 is grown over the entiresurface by the sputtering method, a seed copper film 15 is formed by thesputtering method and then a copper film 16 is formed by the platingmethod. For the material of the barrier metal film 14, metal materialssuch as Ta, TaN, W, WN, Ti and TiN can be used. In the presentembodiment, copper is employed as the interconnection material, althougha copper alloy may be also used.

[0058] Subsequently, the wafer surface is polished by the CMP method sothat a copper interconnection, as shown in FIG. 1(b), may be formed.Hereat, by the effect of an oxidizing agent contained in a CMO slurry,the surface of the copper interconnection 17 may be oxidized to formcopper oxide 21. Accordingly, a cleaning to remove this copper oxide 21is carried out. For the cleaning agent, a solution containing carboxylicacid such as oxalic acid, maleic acid, succinic acid or acetic acid ispreferably used.

[0059] After the cleaning, with carbon oxide removed, a clean surface ofthe copper interconnection 17 is exposed (FIG. 1(c)). Next, a treatmentwith an anticorrosive is performed so as to adhere the anticorrosive 22onto the surface of the copper interconnection 17 (FIG. 2(a)). Asexamples of the anticorrosive 22, as described above, there can be givenBTA and its derivatives, and uric acid and its derivatives. By makingthe anticorrosive 22 adhered thereto, copper can be well protected fromoxidation, even if the wafer is exposed to the air or left in the airfor several days.

[0060] Next, by heating the wafer, the anticorrosive 22 is vapourized(FIG. 2(b)). For example, when BTA is utilized as the anticorrosive, BTAcan be removed almost completely by a heating treatment at a temperatureequal to or higher than 200° C. This heating treatment for detachment ofthe anticorrosive is conducted preferably at a temperature of 200-500°C., and more preferably at a temperature of 300-450° C. Such a treatmentcan effectively detach the anticorrosive therefrom without affecting theelements therein adversely.

[0061] At this stage, the surface of the copper interconnection 17 ismade to be, in the absence of copper oxide and anticorrosive, in a cleanstate. In such a state, the copper surface is subjected to a nitridingtreatment. In the present embodiment, a plasma treatment is performed,using a source gas containing nitrogen and ammonia. With this plasmatreatment, a copper nitride layer 24 is formed on the surface of thecopper interconnection 17 (FIG. 2(c )). An example of conditions for theplasma treatment is shown below. Ammonia flow rate 50-5,000 sccmNitrogen flow rate 0-5,000 sccm (A flow rate ratio of ammonia tonitrogen is preferably set to be 0.01-1.0.) Pressure 1-10 TorrHigh-frequency power 100-1,000 W, preferably 100-500 W Substratetemperature 300-450° C., preferably 350-400° C. Treatment time period 1sec-10 min

[0062] In this plasma treatment, it is preferable to use a source gascomprising a nitrogen element and more preferable to use the gas furthercomprising a hydrogen element to provide a reducing nature. In this way,a copper nitride layer of high quality can be formed without damagingthe surface of the copper-containing film. For a source gas, a mixed gasof nitrogen and hydrogen, a mixed gas of ammonia and nitrogen and mixedgases in which other components are appropriately added into either ofthese above mixed gases can be preferably used. Among these, a mixed gasof ammonia and nitrogen is particularly preferable, because, with this,a copper nitride layer of high quality can be formed well under control.Hereat, a ratio of the amount (volume ratio) of ammonia to the wholemixed gas is set to be preferably 1-50 %. This setting can prevent thedegradation of the copper surface and, at the same time, facilitate toform a copper nitride layer of high quality.

[0063] Next, on the copper interconnection 17, a silicon nitride film 18is formed as a copper-diffusion prevention film. The silicon nitridefilm 18 can be formed by the plasma CVD (Chemical Vapour Deposition)method. The conditions of the film growth can be set, for instance, asfollows. SiH₄ flow rate 50-2,000 sccm, preferable 50-300 sccm Ammoniaflow rate 10-2,000 sccm (A flow rate ratio of ammonia to nitrogen ispreferably set to be 0.01-0.7.) Pressure 1-10 Torr High-frequency power100-1,000 W, preferably 100-500 W Substrate temperature 300-450° C.,preferably 350-400° C.

[0064] In this step of film growth, silicon is diffused, through thecopper nitride layer 24, into the copper interconnection 17, to form acopper silicide layer 25 (FIG. 3(a)). Hereat, the presence of the coppernitride layer 24 can suppress diffusion of silicon from the siliconnitride film 18 into the copper interconnection 17 and, therefore, thefilm thickness of the copper silicide layer becomes less, compared withthe case the copper nitride layer 24 is not provided. Further, becausethe plasma treatment is carried out, as described above, in a statewhere copper oxide on the surface of the copper interconnection 17 isremoved, the copper nitride layer 24 can be formed homogeneously to anuniform thickness. Therefore, it is possible to suppress the increasesin interconnection resistance and contact resistance and, at the sametime, achieve an improvement of the interconnection lifetime.

[0065] Hereat, both of the plasma treatment and the film growthdescribed above are carried out, using a parallel plate type plasmageneration equipment. Within this plasma generation equipment, the stepsfrom the step of a heating treatment to make the anticorrosive detachedto the step of formation of a silicon nitride film are performed. Sincethe vacuum state is maintained throughout these steps, the oxidation ofthe copper surface can be prevented from occurring and the nitridingtreatment can be conducted, while the clean surface thereof ismaintained.

[0066] Next, after an interlayer insulating film 19 is formed fromsilicon oxide (FIG. 3(b)), a via hole is formed by dry etching. Firstly,as shown in FIG. 4(a), an interlayer insulating film 19 is etched andthen, as shown in FIG. 4(b), a silicon nitride film 18 is etched toexpose the copper interconnection 17 at the bottom section of the hole.Hereat, in order to expose the copper interconnection 17 for sure, acertain overetching is, in general, required. In the present embodiment,because the copper nitride layer 24 is homogeneously formed to a uniformthickness as described above, the silicon nitride film 18 can be alsoformed to a uniform thickness well under control. The overetching timeperiod can be, therefore, held down to the minimum.

[0067] After that, by filling up the inside of the via hole with metalsuch as copper or tungsten, an interlayer connecting plug 27 is formed,and, thus, forming a multi-layered interconnection structure (FIG.4(c)).

[0068] The above description is made for an example of a methodemploying a series of steps wherein, after forming a copperinterconnection 17, copper oxide is removed by a cleaning agent, and,then, after an anticorrosive treatment is conducted, a nitridingtreatment is carried out. It is, however, possible not to include thestep of a cleaning or an anticorrosive treatment in a manufacturingmethod of the present invention. In such a case, after growing acopper-containing film, the surface of the copper-containing film issubjected to a nitriding treatment without being exposed to anoxygen-containing atmosphere. For instance, there can be employed amanufacturing method in which, after a copper film is grown and thenpatterned by means of etching or the like, it is subjected to anitriding treatment, while keeping as it is, even without taking outfrom a plasma chamber. This makes the nitriding treatment applied to thesurface in a state where no copper oxide is substantially formed so thata copper silicide layer can be formed homogeneously to a thin uniformthickness, allowing to achieve both a lowering of the electricalresistance and an improvement of the interconnection lifetime, at thesame time.

EXAMPLE 1

[0069] Using a method of manufacturing a semiconductor device accordingto the present invention, copper interconnections were formed and theirinterconnection lifetimes and resistances were evaluated. The method offabricating the copper interconnection is described below. First, by theplasma CVD method, a silicon oxide film was formed on a silicon wafer.Next, by dry etching, a plurality of interconnection trenches patternedinto a prescribed shape were formed. Next, after a barrier metal filmwas formed from Ta by the sputtering method, a seed copper film and aplating copper film were formed in this order.

[0070] Subsequently, the wafer surface was polished by the CMP method soas to leave copper inside of the interconnection trenches, and thereby acopper interconnection was formed. Next, for the purpose of removingpolishing grains, particles such as polishing shavings, metals andslurries, which were adhered onto the surface of the semiconductorwafer, the following steps of cleaning were performed.

[0071] First, a scrub cleaning was made. That is, particlecontaminations were removed by moving a rotating brush, while spraying acleaning agent made of electrolytic ionized water onto the brush. Next,a spin cleaning was made. In this step, while rotating the semiconductorwafer, a cleaning agent made of an aqueous solution containing 0.03 wt.% of oxalic acid was sprayed thereto for 10 seconds to remove copperoxide and then rinsing with pure water was carried out.

[0072] Next, an anticorrosive treatment was made. The agent for theanticorrosive treatment used herein had the following components.Benzotriazole 0.1 wt. % Water the rest

[0073] While rotating the semiconductor wafer, this agent for theanticorrosive treatment was sprayed onto the wafer surface with a flowrate of 1 liter/min for 10 seconds, and thereby an anticorrosivetreatment was applied onto a Cu film. After that, the step of spinrinsing/drying, wherein after rinsing with pure water was conducted for15 seconds, drying was made, was performed.

[0074] Subsequently, a plasma treatment was carried out, using a mixedgas of ammonia and nitrogen, and the surface of the copperinterconnection was nitrided. After that, using a source gas made ofSiH₄, ammonia and nitrogen, a silicon nitride film was formed, by theplasma CVD method, to a thickness of 50 nm on the copperinterconnection. After that, an interlayer insulating film was formedthereon, and a plug to bring into contact with the copperinterconnection was set, whereby a copper interconnection for theevaluation was accomplished.

[0075] Case 1 for Comparison

[0076] Copper interconnections were formed in the same way as Example 1except that, after the oxalic acid treatment, not a BTA treatment butonly an ammonia plasma treatment was performed and thereafter a siliconnitride film was formed.

[0077] Case 2 for Comparison

[0078] Copper interconnections were formed in the same way as Example 1except that, after the oxalic acid treatment, not an ammonia plasmatreatment but only a BTA treatment was performed and thereafter asilicon nitride film was formed.

[0079] The copper interconnections fabricated as described in Example 1and Cases 1 and 2 for Comparison have planar structures shown in FIG. 6(a) and (b). The interconnection resistances and the interconnectionlife times for these copper interconnections were evaluated. Withrespect to the interconnection resistance, the evaluation was madethrough the value of resistance (E1/11) which was obtained by making anelectric current (I1) flow between terminals for measurement P3-P4 ofFIG. 6(a), while increasing from 0 A to 1 mA, and measuring thepotential difference (E1) generated thereat between both ends P1-P2 ofthe measuring element. Regarding the interconnection lifetime, theevaluation was made through the measurement of the time period for thedeviation of the value of resistance (E2/I2) to reach 3%, owing to thedegradation, when a given current (I2) in the range of 0.01 mA-10 mA waskept to flow between terminals for the measurement P5-P6 of FIG. 6(b) ina given atmosphere (at a given temperature and such) and the potentialdifference (E2) generated between P7-P8 was measured.

[0080] The results are shown in FIG. 7 and FIG. 8. In both of thesegraphs, the value of Example 1 is taken as 1, and the values of Casesfor Comparison are expressed in reduced values, respectively. For theinterconnection resistance in FIG. 7, the lower its value is, the betterit is. For the interconnection lifetime in FIG. 8, the higher its valueis, the better it is. Case 1 for Comparison has excellentinterconnection resistances but their variations among elements areconsiderable and besides the interconnection lifetimes are short.Meanwhile, Case 2 for Comparison has the long interconnection lifetimesbut large interconnection resistances with substantial variations. Asagainst these, it is clearly demonstrated that the interconnections ofExample 1 have both excellent interconnection lifetimes andinterconnection resistances and besides variations in interconnectionresistances among elements are small.

[0081] Case 1 for Reference

[0082] On a silicon wafer, a silicon oxide film is formed and thereon acopper plating film is formed over the entire surface. Following that,after the copper surface was polished by the CMP method, for the purposeof removing polishing grains, particles such as polishing shavings,metals and slurries, the following steps of cleaning were performed.

[0083] First, a scrub cleaning was made. That is, particlecontaminations were removed by moving a rotating brush, while spraying acleaning agent made of electrolytic ionized water onto the brush. Next,a spin cleaning was made. In this step, while rotating the semiconductorwafer, a cleaning agent made of an aqueous solution containing 0.03 wt.% of oxalic acid was sprayed thereto for 10 seconds to remove metalcontaminations which are CuO lying on the surface, and then rinsing withpure water was carried out.

[0084] Next, an anticorrosive treatment was made. The agent for theanticorrosive treatment used herein had the following components.Benzotriazole 0.1 wt. % Water the rest

[0085] While rotating the semiconductor wafer, this agent for theanticorrosive treatment was sprayed onto the wafer surface with a flowrate of 1 liter/min for 10 seconds, and thereby an anticorrosivetreatment was applied onto a Cu film. The wafer in this state isdesignated as Sample 1.

[0086] Sample 1 is further subjected to a plasma treatment under thefollowing conditions and, with the surface of the copper film thereinbeing nitrided, is designated as Sample 2. Flow gas Ammonia and nitrogenThe total flow rate 5,000 sccm Flow rate ratio of ammonia to nitrogen is1 to 50. Pressure  5 Torr High-frequency power 200 W Substratetemperature 400° C. Treatment time period

[0087] 20 seconds in a state without applying high-frequency power, and5 seconds in a state with applying high-frequency power

[0088] Sample 1 and Sample 2 obtained as described above are eachsubjected to a treatment for the initial stage of the steps of forming asilicon nitride film by the plasma CVD method. That is, SiH₄ was addedto the above flow gas in the atmosphere at 400° C. and held for 5seconds. The pressure was set to be 5 Torr and the high-frequency power,200 W.

[0089] The occupation ratios of silicide formed on the surface of thecopper film after the above treatment was completed were observed forrespective samples. The observation was made by applying wet etchingwith a mixed solution of ammonia and hydrogen peroxide to the copperfilms after the above treatment. While copper and copper oxide aresoluble in the above mixed solution, copper silicide is insoluble.Therefore, the insoluble portion signifies copper silicide. Whenelementary analysis of the insoluble portion was conducted by the SIMS(Secondary Ion Mass Spectroscopy), copper and silicon were actuallydetected. On the basis of results from such observations, an occupationratio of the copper silicide area that is insoluble in etching withrespect to the whole area of the copper film that has been originallypresent is defined as a silicide occupation ratio. The results of theexperiments are shown in FIG. 9. It is evident that the formation ofsilicide was well suppressed in Sample 2 whose copper surface wasnitrided with the ammonia plasma treatment. These results of theexperiments confirm that nitridation of the copper surface suppressescopper silicide formation.

What is claimed is:
 1. A method of manufacturing a semiconductor device;which comprises the steps of: forming a copper-containing film on asemiconductor substrate; removing, with a cleaning agent, a copper oxideon a surface of said copper-containing film; applying a nitridingtreatment to the surface of said copper-containing film from which thecopper oxide has been removed; and forming a copper-diffusion preventionfilm comprising a silicon on said copper-containing film which has beensubjected to the nitriding treatment.
 2. A method of manufacturing asemiconductor device according to claim 1, wherein, following the stepof removing copper oxide on the surface of said copper-containing film,the step of applying the nitriding treatment to the surface of saidcopper-containing film is performed, without allowing the semiconductorsubstrate on which said copper-containing film from which copper oxidehas been removed is formed to be exposed to an oxygen-containingatmosphere.
 3. A method of manufacturing a semiconductor deviceaccording to claim 1, wherein the nitriding treatment applied to thesurface of said copper-containing film is effected by a plasma treatmentwith a source gas comprising a nitrogen element being used.
 4. A methodof manufacturing a semiconductor device; which comprises the steps of:forming a copper-containing film on a semiconductor substrate; removinga copper oxide on a surface of said copper-containing film; applying ananticorrosive treatment to the surface of the copper-containing film,with an anticorrosive-containing solution being used; carrying out aheating treatment to detach the anticorrosive which is adhered onto thesurface of the copper-containing film and, subsequently, applying anitriding treatment to the surface of said copper-containing film; andforming a copper-diffusion prevention film comprising a silicon on saidcopper-containing film which has been subjected to the nitridingtreatment.
 5. A method of manufacturing a semiconductor device accordingto claim 4, wherein the step of said heating treatment is carried out ina vacuum and, thereafter, keeping the vacuum as it is, the step ofapplying the nitriding treatment to the surface of saidcopper-containing film is performed.
 6. A method of manufacturing asemiconductor device according to claim 4, wherein the nitridingtreatment applied to the surface of said copper-containing film iseffected by a plasma treatment with a source gas comprising a nitrogenelement being used.
 7. A method of manufacturing a semiconductor device;which comprises the steps of: forming a copper-containing film on asemiconductor substrate; applying a nitriding treatment to the surfaceof said copper-containing film without allowing the semiconductorsubstrate to be exposed to an oxygen-containing atmosphere; and forminga copper-diffusion prevention film comprising a silicon on saidcopper-containing film which has been subjected to the nitridingtreatment.
 8. A method of manufacturing a semiconductor device accordingto claim 7, wherein the nitriding treatment applied to the surface ofsaid copper-containing film is effected by a plasma treatment with asource gas comprising a nitrogen element being used.